Recent temperature increases have elicited strong phenological shifts in temperate tree species, with subsequent effects on photosynthesis. Here, we assess the impact of advanced leaf flushing in a winter warming experiment on the current year's senescence and next year's leaf flushing dates in two common tree species: Quercus robur L. and Fagus sylvatica L. Results suggest that earlier leaf flushing translated into earlier senescence, thereby partially offsetting the lengthening of the growing season. Moreover, saplings that were warmed in winter-spring 2009-2010 still exhibited earlier leaf flushing in 2011, even though the saplings had been exposed to similar ambient conditions for almost 1 y. Interestingly, for both species similar trends were found in mature trees using a long-term series of phenological records gathered from various locations in Europe. We hypothesize that this longterm legacy effect is related to an advancement of the endormancy phase (chilling phase) in response to the earlier autumnal senescence. Given the importance of phenology in plant and ecosystem functioning, and the prediction of more frequent extremely warm winters, our observations and postulated underlying mechanisms should be tested in other species.climate change | tree phenology | spring flushing | leaf senescence L eaf phenology of temperate trees has recently received particular attention because of its sensitivity to the ongoing climate change (1-3), and because of its crucial role in the forest ecosystem, water and carbon balances, and species distribution (4-6).A wide variety of methods, such as long-term phenological records (7), indirect measurements of ecosystem greening by remote sensing using satellites or webcam digital images (8-10), and modeling approaches (11-13), have been applied to monitor and study phenological changes. These different approaches, conducted at different spatial scales (from individual plants to biomes), have documented a clear advancement of leaf flushing in temperate climate zones and, to a lesser extent, a delay in leaf senescence (14,15). Furthermore, various temperature manipulation experiments have simulated the impact of future winter warming on leaf phenology and confirmed an advancement in the timing of leaf flushing in response to warming (16-18). However, the response of leaf flushing to climate warming is highly nonlinear (16,19,20), because trees also depend on cold temperatures to break bud dormancy (21-23). This chilling requirement may not (fully) be met in a warming climate, especially at the southern edges of species distribution ranges (5,24,25).Most previous phenological studies have focused on specific phenophases, but how a phenological change (e.g., advanced leaf flushing) affects subsequent phenological events is rarely investigated. Nonetheless, the annual growth cycle of boreal and temperate trees forms an integrated system, where one phenophase in the cycle can affect the subsequent phases (26, 27). Such carryover effects have already been detected in fruit and nu...

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have stimulated studies on the response of terrestrial ecosystems to this global change. Experiments have likewise addressed the importance of species numbers for ecosystem functioning. There is, however, little knowledge on the interplay between warming and species richness. During three years, we grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures (unheated), while the other half were warmed by 3 • C (heated). Equal amounts of water were added to heated and unheated communities, so that warming would imply drier soils if evapotranspiration was higher. Biomass production was decreased due to warming, both aboveground (-29%) and belowground (-25%), as negative impacts of increased heat and drought stress in summer prevailed. Complementarity effects, likely mostly through both increased aboveground spatial complementarity and fa-cilitative effects of legumes, led to higher shoot and root biomass in multi-species communities, regardless of the induced warming. Surprisingly, warming suppressed productivity the most in 9-species communities, which may be attributed to negative impacts of intense interspecific competi-Correspondence to: H. J. De Boeck (hans.deboeck@ua.ac.be) tion for resources under conditions of high abiotic stress. Our results suggest that warming and the associated soil drying could reduce primary production in many temperate grasslands , and that this will not necessarily be mitigated by efforts to maintain or increase species richness.

Summary• This paper presents the results of 2 yr of CO 2 flux measurements on grassland communities of varying species richness, exposed to either the current or a warmer climate.• We grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers. Half of these chambers were exposed to ambient air temperatures, while the other half were warmed by 3 ° C. Equal amounts of water were added to heated and unheated communities, implying drier soils if warming increased evapotranspiration. Three main CO 2 fluxes (gross photosynthesis, above-ground and below-ground respiration) were measured multiple times per year and reconstructed hourly or half-hourly by relating them to their most important environmental driver.• While CO 2 outputs through respiration were largely unchanged under warming, CO 2 inputs through photosynthesis were lowered, especially in summer, when heat and drought stress were higher. Above-ground CO 2 fluxes were significantly increased in multispecies communities, as more complementary resource use stimulated productivity. Finally, effects of warming appeared to be smallest in monocultures.• This study shows that in a future warmer climate the CO 2 sink capacity of temperate grasslands could decline, and that such adverse effects are not likely to be mitigated by efforts to maintain or increase species richness.

Violence in the Rakhine State of Myanmar has led to a humanitarian crisis as Rohingya people flee across the border to Bangladesh (1). With the rapid influx of nearly 700,000 arrivals between August 2017 and the beginning of 2018, the Bangladeshi city of Cox's Bazar is now under severe strain from a Rohingya population of almost 1 million, one of the largest concentrations of refugees in the world (2). The crisis seized global attention, and the international response was rapidly escalated to a Level 3 emergency (3). In addition to the humanitarian challenges, the mass influx of Rohingya refugees has resulted in environmental degradation both within the refugee camps and in the surrounding areas (2). The expansion of existing campsites has led to more than 2000 ha of forest loss in the Cox's Bazar region (4). Expansion of the old Kutupalong camp blocked the only corridor used by the globally endangered Asian elephant as a migration route and trapped about 45 elephants in the western side of the camp (5). The latest Rohingya settlement has also amplified humanelephant conflict in the area, with 13 human casualties so far (6). The remaining elephant habitat is under severe pressure from uncontrolled fuelwood collection in the forest (7). The pressure on forests has caused tensions with local

The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide-CO2, methane-CH4 and nitrous oxide-N2O) remain poorly understood in highly complex ecosystems such as tropical forests. We used 240 individual flux measurements of these three GHGs from different soil types, at three topographical positions and in two extreme hydric conditions in the tropical forests of the Guiana shield (French Guiana, South America) to (1) test the effect of topographical positions on GHG fluxes and (2) identify the soil characteristics driving flux variation in these nutrients-poor tropical soils. Surprisingly, none of the three GHG flux rates differed with topographical position. CO2 effluxes covaried with soil pH, soil water content (SWC), available nitrogen and total phosphorus. The CH4 fluxes were best explained by variation in SWC, with soils acting as a sink under drier conditions and as a source under wetter conditions. Unexpectedly, our study areas were generally sinks for N2O and N2O fluxes were partly explained by total phosphorus and available nitrogen concentrations. This first study describing the spatial variation of soil fluxes of the three main GHGs measured simultaneously in forests of the Guiana Shield lays the foundation for specific studies of the processes underlying the observed patterns.

Background and aims Biological fixation of atmospheric nitrogen (N 2) is the main pathway for introducing N into unmanaged ecosystems. While recent estimates suggest that free-living N fixation (FLNF) accounts for the majority of N fixed in mature tropical forests, the controls governing this process are not completely understood. The aim of this study was to quantify FLNF rates and determine its drivers in two tropical pristine forests of French Guiana. Methods We used the acetylene reduction assay to measure FLNF rates at two sites, in two seasons and along three topographical positions, and used regression analyses to identify which edaphic explanatory variables,

Predicting future ecosystem functioning requires a mechanistic understanding of how plants cope with different stressors under future climate conditions with elevated CO2 concentrations and warmer temperatures. Nonetheless, studies of stress responses under combined elevated CO2 and warming remain scarce. We assembled grassland communities in sunlit, climate-controlled greenhouses and subjected these to three stressors (drought, zinc toxicity, nitrogen limitation) and their combinations. Half of the communities were exposed to ambient climate conditions (current climate) and the other half were continuously kept at 3 degrees C above ambient temperatures and at 620 ppm CO2 (future climate). Across all stressors and their combinations, future climate-grown plants coped better with stress, i.e. above-ground biomass production was reduced less in future than in current climate. Among several tested potential biochemical and ecophysiological stress-relief mechanisms, we found three mutually non-exclusive mechanisms underpinning an improved stress protection under future climate conditions: (i) altered sugar metabolism; (ii). up-regulated levels of total antioxidant capacity and polyphenols; and (iii) more efficient use of ascorbate and glutathione as antioxidants. (C) 2014 The Authors. Published by Elsevier B.V. All rights reserved

Abstract. Measuring in situ soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) continuously at high frequency requires appropriate technology. We tested the combination of a commercial automated soil CO2 flux chamber system (LI-8100A) with a CH4 and N2O analyzer (Picarro G2308) in a tropical rainforest for 4 months. A chamber closure time of 2 min was sufficient for a reliable estimation of CO2 and CH4 fluxes (100 % and 98.5 % of fluxes were above minimum detectable flux – MDF, respectively). This closure time was generally not suitable for a reliable estimation of the low N2O fluxes in this ecosystem but was sufficient for detecting rare major peak events. A closure time of 25 min was more appropriate for reliable estimation of most N2O fluxes (85.6 % of measured fluxes are above MDF ± 0.002 nmol m−2 s−1). Our study highlights the importance of adjusted closure time for each gas.